Reaction of the previously reported Cp*Ti(N
tBu)Cl(py) (
1) with bulky
ortho-substituted anilines ArNH
2afforded the corresponding aryl imido derivatives Cp*Ti(NAr)Cl(py) (Ar = 2,6-C
6H
3iPr
2 (
2), 2,6-C
6H
3Br
2 (
3), 2-C
6H
4tBu (
4), and 2-C
6H
4iPr (
5)). Reaction of
2 with B(C
6F
5)
3 in C
6D
6 or heating in vacuo at200
C afforded the imido-bridged dimer Cp*
2Ti
2(
-N-2,6-C
6H
3iPr
2)
2Cl
2 (
8). Activation of
1-
5 withMAO gave moderately active catalyst systems for the polymerization of ethylene in contrast to thepreviously reported, highly active titanium imido systems Ti(Me
3[9]aneN
3)(NR)Cl
2/MAO and Ti{HC(Me
2pz)
3}(NR)Cl
2/MAO, which are isolobal and isoelectronic with
1-
5. The Cp*-supported precatalystproductivities were sensitive to both the imido N-substituents and initial precatalyst/cocatalyst concentrations. Depending upon the imido N-substituents and initial precatalyst/cocatalyst concentrations,polyethylene with unimodal (either rather low or very high molecular weight) or bimodal molecularweight distributions can be obtained. Excess AlMe
3 suppresses catalyst productivity but does not affectthe overall molecular weight distribution in the system evaluated (
1/MAO). Both chain transfer to aluminumand
-hydrogen transfer appear to be active pathways for formation of the low molecular weight fractionsof the polymers formed with
1-
5/MAO. Under otherwise identical polymerization conditions the catalystsystems
2/MAO and
8/MAO had comparable productivities and gave polyethylene with very similarmolecular weight and molecular weight distributions, suggesting a potential role for binuclear species inthe catalyst systems
1-
5/MAO.